In a conventional technique in the field of a radar, a radar system has been developed which performs beam synthesis by executing the so-called “distributed aperture process” which controls and adds the phases and amplitudes of signals from a plurality of sub-modules arranged (fixed) in known optional positions, as shown in FIG. 1. However, there is a following problem in such a technique.
First, there is a problem of “grating lobe” in which the beam of the same intensity as in a desired direction is outputted because equal phase planes are collectively aligned even in a side direction when an interval between elements is longer than a half wavelength. Therefore, the suppression of grating lobe becomes necessary. However, in case that sub-modules are unevenly arranged, the suppression of grating lobe is not enough only by the control of the amplitude and phase, depending on the arrangement of the sub-modules.
Also, when a sub-module interferes with a sight of another sub-module (a line of sight of a beam), the synthetic beam reduces.
Also, when a performance degradation or a function stop occurs in a part of the sub-modules, the whole performance (the radar performance by the synthetic beam) sometimes degrades greatly.
As a prior art in the technical field, Patent Literature 1 (JP 2010-32497A) discloses a radar apparatus and a method of forming a reception beam. In the prior art, an active phase array antenna is divisionally formed in an optional place, to realize the characteristics of the distributed aperture antenna, which results in the superior performance of the radar.